The general objective of this study is further understanding of interactions between those microorganisms indigenous to the oral microflora particularly those observed to be present in instances of gingival inflammation. We are specifically interested in explanations for population dominance, population shifts and in the influence of one bacterial species on another during the course of such diseases. We will determine the amount of tissue reactive substance formed by specific populations and determine relationships of bacterial products to population dynamics. The ultimate objective is, of course, a more complete understanding of the etiology of chronic inflammatory periodontal disease.